The present disclosure is directed generally to an apparatus and method for manufacturing a photovoltaic cell, and specifically to an apparatus and method for manufacturing a silver copper indium gallium selenide absorber layer by reactive sputtering.
A “thin-film” photovoltaic material refers to a polycrystalline or amorphous photovoltaic material that is deposited as a layer on a substrate that provides structural support. The thin-film photovoltaic materials are distinguished from single crystalline semiconductor materials that have a higher manufacturing cost. Some of the thin-film photovoltaic materials that provide high conversion efficiency include copper-indium-gallium-chalcogenide material, such as copper indium gallium selenide (CIGS).
Thin-film photovoltaic cells (also known as solar cells) may be manufactured using a roll-to-roll coating system based on sputtering, evaporation, or chemical vapor deposition (CVD) techniques. A thin foil substrate, such as a foil web substrate, is fed from a roll in a linear belt-like fashion through the series of individual vacuum chambers or a single divided vacuum chamber where it receives the required layers to form the thin-film photovoltaic cells. In such a system, a foil having a finite length may be supplied on a roll. The end of a new roll may be coupled to the end of a previous roll to provide a continuously fed foil layer.
The processing rate of the roll is determined by the deposition rates of the electrode and semiconductor materials deposited on the foil web substrate. It is well known, however, that performance metrics of the photovoltaic cell, such as efficiency, open circuit voltage, closed circuit current density, and fill factor critically depends on the crystalline quality of the deposited semiconductor material. Generally, semiconductor materials deposited at a low deposition rate provides larger grain sizes and superior performance. Thus, a method for depositing a high quality crystalline material at a high deposition rate is desirable.